(1) Field of the Invention
The present invention relates to an apparatus for controlling the idling speed in an internal combustion engine, the apparatus having two air passages bypassing a throttle valve disposed within an intake air passage.
(2) Description of the Related Art
In an internal combustion engine, in order to control the idling (engine) speed, a first bypass air passage bypassing a throttle valve is provided. The first bypass air passage is controlled in accordance with the engine speed. That is, when the engine speed exceeds the upper limit of a predetermined range, the first bypass air passage is closed, and when the engine speed becomes lower than the limit of a predetermined range, the first bypass air passage is opened, thus stabilizing the idling speed.
In the above-mentioned engine, when an electrical load such as an air conditioner or a power steering system is turned ON, the idling speed is usually not high enough to allow a generator (alternator) to provide the battery with a full replacement charge, thus draining the battery-charge. Further, when a vehicle has an automatic transmission and the gear position is changed from neutral (N) to drive (D) the idling speed may be reduced by the load placed on the engine. To avoid these disadvantages, a second bypass air passage bypassing the throttle valve is provided to further enhance the idling speed.
In the above-mentioned engine having two bypass air passages, however, when both of the bypass air passages are opened sometimes the engine speed increases to close the first bypass air passage, and immediately thereafter, the electrical load is turned OFF to close the second bypass air passage. In this case, the engine speed may be remarkably reduced, thus inviting engine stalling at worst.
Further, when the electrical load such as the air conditioner is turned OFF, the solenoid switch thereof is immediately turned OFF, however, there is a delay in closing the second bypass air passage. Therefore, even when the engine speed is slightly lower than the upper limit of the predetermined range, and in addition, the electrical load is turned OFF, the engine speed increases due to the delay in the closing of the second bypass air passage, so that the engine speed exceeds the upper limit of the predetermined range. As a result, the first bypass air passage is closed and undershoot of the engine speed occurs, also inviting engine stalling at worst.